Years ago, a wealthy family lived in the Alden house. Suddenly, however, the Shaws moved to France, and that's when Mr. Alden bought the house. But that was over forty years ago, and very few people even remember the Shaws today. But some old memories are about to be stirred up, when Benny and his Canadian friend Rory discover an old diary left by a young girl all those many years ago. The boxcar children are suddenly in the midst of an ancient treasure hunt, searching for a priceless coin collection. The clues are puzzling, but time is their greatest enemy. Will Stephanie Shaw's notes withstand the test of time so the children can solve the mystery?